1. Field of the Invention
The invention relates to a static mixer for an exhaust gas system of an internal combustion engine which is disposed in an exhaust gas pipe of the internal combustion engine and which consists of a plurality of flow guide elements that influence the flow of a fluid stream. The flow guide elements are disposed on a central center element and extend outwardly in the direction of the inner wall of the exhaust gas pipe. The flow guide elements have a section in the flow direction of the fluid stream that is inclined at a predetermined angle relative to the flow guide elements.
2. The Prior Art
It is known that the reduction of nitrogen oxide emissions of the exhaust gases of an internal combustion engine takes place by means of selective catalytic reduction (SCR). In this connection, a suitable reduction agent, such as liquid urea or gaseous ammonia, is introduced into the exhaust gas stream in the case of a lean exhaust gas composition, for the purpose of NOx reduction. Usually, a static mixer is used to mix the reduction agent with the exhaust gas, by means of which mixer a desired distribution of the reduction agent in the exhaust gas stream is supposed to be achieved, for the purpose of efficient exhaust gas purification.
German Patent No. DE 10 2007 012 790 B4 describes a static mixer for mixing a reduction agent with the exhaust gas stream of an internal combustion engine, which mixer is disposed in the exhaust gas pipe of the internal combustion engine, and consists of a plurality of flow guide elements that influence the flow of a fluid stream, configured in the manner of vanes. The flow guide elements are disposed on a central center element and extend in the direction of the inner wall of the exhaust gas pipe. The flow guide elements consist of a carrier element on which vane-like sections are disposed, to influence the flow. In this connection, the vane-like sections are disposed on the carrier element in such a manner that they have a predetermined angle relative to the flow direction of the exhaust gas stream.
German Patent Application No. DE 100 60 808 A1 describes a mixing device which consists of multiple guide blades. The guide blades are disposed in the exhaust gas pipe, on a central center element. The flow direction is deflected as the exhaust gas flows through the mixing device by the guide blades configured in the manner of blades.
U.S. Pat. No. 4,848,920 describes a static mixer which is supposed to produce a homogeneous media stream. This mixer has a number of ribs disposed around a central hub, spaced apart from one another at angles. Additional vane elements are formed onto these ribs.
German Patent Application No. DE 10 2008 017 395 A1 describes a mixer that is produced from only a single sheet-metal body. The mixer consists of a pipe body having radially projecting blades on the axial ends. The blades are disposed and configured in such a manner that they are set at an angle relative to an axial direction of the pipe body. As a result, the flow resistance is increased in the region of the blades, and swirling is produced. This swirling of the exhaust gas stream supports the evaporation of the liquid reduction agent, if applicable, and improves the homogenization of the mixture.
German Patent No. DE 10 2006 058 715 B3 describes a static mixer for an exhaust gas system of an internal combustion engine, which mixer consists of a plurality of flow elements that influence the flow of the exhaust gas stream. The flow guide elements are formed by single-vane guide vanes that project away from a mixer plane in the flow direction of the exhaust gas. The vanes are disposed in multiple guide vane rings about a mixer center point, and are inclined away from the mixer center point, proceeding from their connection point to the mixer radially to the outside, so that the exhaust gas stream is forced radially outward by the guide vanes.
The mixers used serve primarily to mix liquid reduction agents with the exhaust gas stream. In addition, the liquid reduction agent is supposed to be evaporated when it impacts the components of the mixer. When gaseous reduction agents are used, sufficient mixing of the gaseous reduction agent with the exhaust gas stream is not possible with the mixers described. Another disadvantage of the mixers is that turbulent flows occur as the result of the flow guide elements or the blades, and these can lead to undesirable back-flow effects. Furthermore, the back-flow effects have a negative impact on the pressure loss above the mixer.